CHEM 242 Final Exam

Why is it necessary to run a geometry optimization before running an NMR or bond order calculation?

if the NMR is run on a non-optimized structure, the results will not be accurate

The "cleanup" button on WebMO is extremely fast because it isn't doing any quantummechanical calculations. What is it doing to generate an initial structure?

It uses VSEPR to determine the number of ideal Hydrogens, ideal bond lengths, and angles

What is the primary safety hazard of isopentyl nitrate in 3-step synthesis?

Isopentyl nitrate is a vasodilator and contributes to shortness of breath

Mechanistically, we approximate NaBH4 as H- (hydride ion). Why is that technically not correct?And despite being incorrect, why is it a convenient approximation?

This is technically not correct because the B-H bond is covalent, not ionic. However, it is a convenient approximation because the B-H bond is polar and the H has a partial negative charge, making it nucleophilic.

What is the specific mechanistic role for the potassium hydroxide in Step 2 of the 3-step synthesis?

The base is needed to generate an enolate ion which is the reactive nucleophile (alternative - they could also describe the E1cB reaction)

If we use a standard inert organic solvent like hexane or ether, the yield of ester is around 50%.If we use acetic acid as the solvent, the yield is over 90%. Why is the yield 50% with inert organicsolvents, and why is it so much higher with acetic acid as the solvent?

The yield is 50% because carboxylic acids and esters have very similar stability/reactivityUsing acetic acid as solvent pushes the equilibrium due to Le Chatelier's principle since we've addedmore reactant

explain why the NMR solvent you used for the esters and unknown labs was deuterated chloroform, CDCl3, and not regular chloroform, CHCl3 or even methylene chloride,CH2Cl2.

The concentration of solvent molecules is much larger than the concentration of your sample. If you used a proton solvent like CHCl3 or CH2Cl2, you would only see your solvent peak and your compound's signals would be barely visible above the baseline.

Safety hazards of nitric acid

corrosive, red fumes, strong oxidizing agent, choking odor

safety hazards of 95% ethanol

extremely flammable and denatured

safety hazards of KOH

corrosive

safety hazards of isopentyl nitrite

vasodilator, shortness of breath

safety hazards of sulfuric acid (H2SO4)

corrosive, highly reactive, toxic if ingested

What is the benefit if refluxing?

refluxing allows us to heat the reaction at a high temperature without evaporating the solvent

what does the drying tube do

prevents moisture from getting in

What is the formula for the index of hydrogen deficiency?

[2C x 2 + 2] - #H's/ 2

Ceric nitrate test

alcohol and phenol

Lucas test

determines whether it is 1, 2, 3

Ferric Chloride Test

Phenol or ester

Tollens Test

aldehyde

nitrous acid test

amines

nitro groups tests

nitro groups

silver nitrate

alkyl halides

Why is the formation of benzyne highly favorable

- diazonium is a good LG and EAS partner

- CO2 is a good leaving group

Why does the reaction need to be dry in ester synthesis?

H2O pushes the reaction backwards

What should the Lucas test tell us?

tertiary and secondary alkyl cations are more stable and will promote a faster reaction

How can you tell which diazonium ion is more stable?

higher Gibbs free energy, less stable, slower decomposition rate

What derivative should you use if you have an aldehyde

semicarbazone/oxime

What derivative should you use if you have a ketone

semicarbazone/oxime

What derivative should you use if you have an amine

acetamides/benzamides

What derivative should you use if you have a carboxylic acid

toluidide/anilides

What derivative should you use if you have an ester

3,5-dinitrobenzoate

How can you force the equilibrium to the product side in ester synthesis?

1. use acetic acid in excess

2. remove water from the reaction

Why is the equilibrium constant close to 1 for ester synthesis?

Carboxylic acids and esters have similar stabilities because their leaving groups have similar abilities so the equilibrium will be close to 1.

Why are intramolecular reactions faster?

Intramolecular reactions only involve 1 molecule so we don't have to wait for 2 molecules to randomly collide.

Why does the color change when the conjugation changes?

Different color of light is absorbed

Why is the reaction between anthranilic acid and isopentyl nitrite spontaneous and endothermic?

it is endothermic because the reaction is forming a highly unstable molecule (benzyne = strained)

however, it is spontaneous because the entropy is increased with the increase in gaseous products.

Is carboxylic acid in the organic or aqueous layer?

aqueous

is the alcohol in the organic or aqueous layer?

organic

Why would neither increasing the temperature of the hot plate nor running the reaction for alonger time result in a higher yield of ester?

The reaction has reached equilibrium. Waiting longer will not change anything and increasing the temperature is not possible because the reaction is already at reflux.

Briefly explain why using the cleanup button would lead to flawed results if used in between a geometry optimization and NMR calculation.

The cleanup button is at a lower level than the actual calculation so using it would lead to flawed results if used between a geometry optimization and NMR calculation.

Why does it not matter if we give energies in kJ/mol to any decimal places?

1 kJ/mol is less than the margin of error of the calculations.

If the y axis value is 100% on IR, what does this tell you about how much light is absorbed by the sample compared to how much light reaches the detector?

No light is absorbed by the sample and all of it reaches the detector

If the y axis value is 0% on IR, what does this tell you about how much light is absorbed by the sample compared to how much light reaches the detector?

all the light is absorbed by the sample and none of it reaches the detector

What should you know about the camphor reduction reaction?

reaction is irreversible and under kinetic control

In ester synthesis, the sulfuric acid is catalytic. Can the nitric acid in this step be used catalytically? Why or why not?

No, nitric acid is an oxidizing agent and we would need a stoichiometric amount to oxidize the alcohol.

Explain why using the cleanup button would lead to flawed results if used in between a geometry optimization and NMR calculation.

cleanup button is a lower level of theory and would undo the work done by the geometry optimization which would lead to flawed NMR results

Why are water soluble compounds water soluble?

They have little to no hydrophobic content

state 2 reasons why some entries on the derivative list were blank

1. the reaction doesn't work

2. derivative too unstable

3. compound was a liquid

What is the specific mechanistic role for the potassium hydroxide in step 2 of 3 step synthesis?

forms enolate ion which is the reactive nucleophile

What is the specific mechanistic role for the sulfuric acid and how does this speed up the reaction in Fischer esterification ?

sulfuric acid protonates the acetic acid C=O which acts as a better electrophile for the alcohol to attack quicker